Introduction
Understanding key properties of paper, such as breaking length and tensile strength, is crucial to ensuring that the paper we produce meets the required quality standards. This training will explain what breaking length is, why it matters for the paper’s strength, and how tensile strength is calculated to assess the paper’s durability.
What is Breaking Length?
Breaking length measures the strength of a sheet of paper. It indicates how long a piece of paper can be suspended vertically before breaking under its own weight.
Simple Definition: The maximum length of paper that will not break when hung by its own weight.
Why It’s Important: The longer the breaking length, the stronger the paper. Stronger paper is essential for products that need to resist tearing or stretching, such as packaging or heavy-duty paper products.
Why is Breaking Length Important for Paper Quality?
Strength of Paper
Breaking length is a direct indicator of the paper’s strength. A higher breaking length means stronger paper, which is crucial for preventing tearing or damage during handling, processing, or use.
Quality Consistency
Ensuring a consistent breaking length throughout production helps maintain overall paper quality. Variations in breaking length can indicate issues with raw materials, machine settings, or production conditions that need to be addressed immediately.
Application Suitability
Different types of paper require different strength levels. For example, packaging paper requires a high breaking length, whereas office paper may need less. Understanding how to monitor and control breaking length ensures we meet the needs of the end-user.
Tensile Strength and Its Relationship to Breaking Length
Tensile strength refers to the force required to break paper when it is stretched. It is closely related to breaking length—the higher the tensile strength, the longer the paper can be before breaking under its own weight.
How is Tensile Strength Calculated?
Tensile strength can be calculated using the formula:
Tensile Strength (N/m) = Breaking Length (meters) × Grammage (g/m²)
Breaking Length: The length at which the paper breaks under its own weight (measured in meters).
Grammage: The weight of the paper per square meter (measured in g/m²).
This formula helps assess the paper’s strength based on its breaking length and weight.
How is Breaking Length Measured in the Mill?
At the production level, breaking length is measured using a specialized device called a Tensile Tester. The process involves:
Preparing the Paper Sample
A sample of paper is cut to a specific size and conditioned (humidity and temperature controlled) for accurate readings.
Performing the Test
The sample is placed in the tensile tester, which applies a pulling force until the paper breaks. The maximum load before breaking is recorded.
Calculating the Breaking Length
Once the breaking force is determined, breaking length is calculated using the formula, factoring in the paper’s grammage.
How Team Members Can Control Breaking Length?
Several factors influence and help maintain the desired breaking length during production:
- Monitor Raw Materials: Consistent pulp quality is essential, as variations in fibre type or length can affect paper strength.
- Adjust Machine Settings: Machine speed, pressure, and temperature impact breaking length. Ensuring optimal settings helps maintain paper strength.
- Check Calendaring: The calendaring process (where paper is smoothed and compressed) can affect strength. Over-compression may reduce tensile strength.
- Grammage Control: Regularly checking grammage ensures it falls within the correct range for the required breaking length. Heavier paper typically has a higher breaking length.
- Quality Control: Regular testing and monitoring throughout production help identify issues early, ensuring consistent quality and preventing defects.
Key Points to Remember
- Breaking length directly affects paper strength—a higher breaking length means stronger paper.
- Tensile strength is linked to breaking length and grammage and is calculated as Breaking Length × Grammage.
- Regular testing and monitoring ensure high-quality paper production and prevent defects.
- Team members play a key role in adjusting machine settings and controlling materials to maintain the proper breaking length.